This application is based on applications No. 11-194551 filed in Japan on Jul. 8, 1999, No. 11-302493 filed in Japan on Oct. 25, 1999, and No. 11-303134 in Japan on Oct. 25, 1999, the contents of which incorporated hereinto by references.
The present invention relates to a display apparatus provided with a plurality of light emitting devices such as light emitting diodes arrayed in a matrix A display panel, and to its method of operation.
Currently, bright red, green, and blue (RGB) light emitting diodes (LEDs) of 1000 mcd or more have been developed, and fabrication of large-scale LED displays has become possible. These LED displays have features such as low power consumption, lightness in weight, and the possibility for thin panel display. Further, demand for large-scale displays, which can be used out doors, has increased dramatically.
Practical large-scale LED displays are configured to fit the installation space by assembling a plurality of LED units. An LED unit is formed from a dot matrix array of RGB LEDs arranged on a substrate board.
Further, an LED display is provided with a driver circuit capable of driving each individual light emitting diode. Specifically, each LED control device, which transmits display data to each LED unit, is connected to the LED display, and a plurality of LED units are connected to form one large-scale LED display. The number of LED units used increases as the LED display becomes larger in scale. For example, a large-scale display can use 300 verticalxc3x97400 horizontal, or 120,000 LED units.
The LED display uses a dynamic driver system as its driver method, and specifically, the display is connected and driven as described below.
For example, in an mxc3x97n dot matrix LED unit, each LED anode in each line is connected to a common source line, and each LED cathode in each column is connected to a common current line. The m-line common source lines are sequentially turned on for display with a prescribed period. For example, m-line common source line switching is performed via decoder circuitry based on the address signal.
However, when LEDs connected to a selected common source line were activated in related art apparatus, charge accumulated in non-activated LEDs connected to unselected common source lines. When these common source lines were then selected, excess current developed as a result of charge built-up during their inactive period. As a result of this problem, LEDs controlled to be off emitted low levels of light and sufficient image contrast could not be obtained. These types of effects caused display quality degradation.
Thus, the first object of the present invention is to reduce the effects of accumulated charge and provide a high quality image display apparatus and its method of operation.
Further, in an LED display, corrected image data are typically used for each LED device to display a high quality image. This is because device-to-device LED variation in brightness, for example, is relatively large.
More specifically, the control circuit has a read-only-memory (ROM) correction data memory section to store correction data corresponding to each LED device. Corrected image data based on the correction data stored in ROM has been used for display.
However, since correction data were stored in ROM in related art apparatus, correction data could not be re-written. Consequently, related art apparatus had the problem that it was necessary to provide a re-writable memory device separate from ROM when different correction data were required.
Thus, the second object of the present invention is to provide an image display apparatus which can store a plurality of correction data in one correction data memory section.
Further, to accurately represent image data on an LED display, the light emission characteristics (driving current vs. brightness characteristics) of each LED device in the image display apparatus must be uniform. However, since LEDs are fabricated on wafers by semiconductor technology, light emission characteristic variation results from fabrication lot-to-lot, wafer-to-wafer, and chip-to-chip. Therefore, it is necessary to correct image data amplitude to compensate for light emission characteristic differences of the LED for each pixel.
An example of related art image data correction is described as follows.
Turning to FIG. 12, a block diagram of an embodiment of a related art LED display is shown. In FIG. 12, 101 is an m-line n-column LED matrix, 107 is a control circuit, 105 is a microprocessor unit (MPU), 106 is a ROM to store correction data, 102 is a common driver circuit, 103 are horizontal driver circuits, 109 are correction circuits to correct image data, and 110 are random access memory (RAM) to temporarily store correction data. The horizontal driver circuits 103, correction circuits 109, and RAM 110 are integrated in LED driver integrated circuits (IC""s) 104 (k) provided for each column of the LED matrix (k=1 to n).
First, prior to display illumination, correction data for the mxc3x97n pixels stored in ROM are transferred to a high speed buffers. RAM 110 are used as the high speed buffers. Correction data transfer is accomplished as follows. First, correction data held in ROM 106 are read out by the MPU 105. The MPU 105 sequentially selects LED driver IC""s 104 (k) via the address bus 111 and sequentially outputs one columns-worth, or m-pixels, of correction data corresponding to each selected column. The correction data output is input to each LED driver IC 104 (k) via the correction data bus 112 and stored in RAM 110 internal to the LED driver IC 104 (k).
When LEDs are illuminated, correction data stored in RAM 110 are sequentially read out by correction circuits 109. The value of input image data (IMDATA) is increased or decreased for each pixel based on the correction data to achieve image data correction. Corrected image data are output to the driver circuits 103, and the driver circuits 103 produce driving current for each LED based on the corrected image data.
However, in the related art LED display described above, a total of mxc3x97n pixels-worth of correction data must be stored in the buffers, or RAM 110, and as display pixel count increases, very large RAM capacity becomes necessary. Further, the operation of correction data read-out from RAM 110 to the correction circuits 109 becomes complicated as the amount of RAM increases. In addition to these problems, both the address bus 111 and the data bus 112 must branch to, and connect with, each of the n driver IC""s 104 (1 to n), thereby making wiring complex and peripheral circuitry large in area.
Thus, the third object of the present invention reflects consideration of these problems, and is to provide an image display
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.
The image display apparatus of the present invention is provided with a dot matrix of light emitting devices, driver circuitry, and a switching circuit section. The dot matrix is a plurality of light emitting devices arranged in a matrix of m-lines and n-columns. One terminal of each light emitting device in each column is connected to a current line, and the other terminal of each light emitting device in each line is connected to a common source line. Driver circuitry controls the display drive to be in an active or inactive state depending on an input illumination signal. In the display drive active state, driver circuitry controls connection of one end of each common source line and each current line according to input display data. The switching circuit section floats the other end of each common source line in the active state and connects the other end of all common source lines to ground in the inactive state.
In this image display apparatus, charge accumulated at light emitting devices and their periphery in the active state, is discharged via the switching circuit section during the inactive state. Consequently, the effects of charge accumulated during active illumination of prescribed light emitting devices are essentially eliminated, and a high quality image display apparatus is realized.
In the image display apparatus of the present invention, driver circuitry can be configured as m-units of current source switching circuits connected to respective common source lines, and a constant current control circuit section. In the active state, a current source switching circuit connects a current source to the common source line selected by an input address signal. The constant current control circuit section is provided with memory circuits, and these memory circuits store pixel level data for n-pixels of sequentially input display data. In the active state, the constant current control circuit section drives a current line for the pixel level width corresponding to pixel level data stored in the memory circuit.
Further, the present invention is a method of operation of an image display apparatus provided with a plurality of light emitting devices arranged in a dot matrix of m-lines and n-columns, wherein one terminal of each light emitting device in each column is connected to a current line, and the other terminal of each light emitting device in each line is connected to a common source line. This method of operation is characterized by inclusion of a step to control active and inactive states according to an illumination control signal which controls the state of illumination, a step to control conduction through one end of each common source line and one end of each current line in the active state based on input display data, and a step to float the other end of each common source line in the active state and ground the other end of each common source line in the inactive state.
In the image display apparatus and method of operation of the present invention, charge accumulated at light emitting devices and their periphery in the active state can be discharged via the switching circuit section during the inactive state. Consequently, the effects of charge accumulated during active illumination of prescribed light emitting devices can essentially be eliminated, and a high quality image display apparatus and method of operation can be offered.
Further, the image display apparatus of the present invention is provided with a display section of light emitting devices arrayed in an m-line by n-column matrix, a correction data memory section to store correction data corresponding to each respective light emitting device, and control and driver circuitry to correct input image data based on the correction data and to display an image on the display section using the corrected image data. The correction data memory section is provided with a single memory unit having a read-only first memory bank, which holds pre-stored first correction data, and a writable second memory bank.
An image display apparatus of this structure can retain first correction data in the first memory bank without erasure, and can use the writable second memory bank to store second correction data, which are different than the first correction data. Depending on requirements, either the first correction data or the second correction data can be selected to revise the image data. In the image display apparatus of the present invention, the correction data memory section can be configured using non-volatile memory which is electrically erasable and writable.
The image display apparatus of the present invention may also be provided with a communication control section. The communication control section can allow writing of second correction data, which are different than first correction data, to the second memory bank, and forbid writing to the first memory bank. It is also desirable to be able to set the writable second memory bank to forbid writing and protect correction data written into that memory bank.
In the correction data memory section of the image display apparatus of the present invention, it is desirable to store correction data for each pixel such that the address corresponds to the light emitting device for each pixel, and the first memory bank and the second memory bank can be distinguished by the highest order address bit. In this manner, lower order address bits can be set for the same read-out address independent of memory bank.
Further, it is desirable to configure the image display apparatus described above in units which display one part of the entire image data. In this manner, the entire image of a large-scale display can easily be assembled from a plurality of these display units.
Further, the image display apparatus of the present invention is provided with:
(a) a display section made up of a plurality of light emitting devices arranged in an m-line by n-column matrix;
(b) a vertical driver section which sequentially selects each line of the display section and sources current to each line;
(c) a horizontal driver section which supplies driving current to each column of the display section according to image data corresponding to the selected line;
(d) an image data correction section which corrects externally input image data according to variations in light emitting device characteristics for each pixel, and outputs corrected data to the horizontal driver section; and
(e) a correction data memory section to hold correction data for image data correction.
The image data correction section reads out one line of correction data from the correction data memory section each time it outputs one line of corrected image data to the horizontal driver section. In this system, the amount of correction data that must be temporarily retained in the image data correction section can be reduced, large amount of memory such as random access memory (RAM) does not need to be used as buffer memory, and image data can be corrected via simple circuit structure.
The image data correction section of the image display apparatus of the present invention is provided with buffer memory to store at least one line of correction data. The image data correction section can read out the next line of correction data from the correction data memory section while it outputs one line of corrected image data to the horizontal driver section. This prevents any display time lag between lines due to image data correction.
In the image display apparatus of the present invention, shift registers can be provided as buffer memory, and correction data can be read via the shift registers by direct sequential shifting one bit at a time. This eliminates the need for data bus line branching to transfer correction data to buffer memory in the correction data memory section, and it also eliminates the need for an address bus to select buffer memory. Therefore, wiring area can be reduced and wiring layout options can be increased.
Still further, in the image display apparatus of the present invention, two stages of interconnected registers can be provided as buffer memory. When the first register outputs one line of correction data, the next line of correction data is read into the second register. Each time output and input of one line of correction data is completed, correction data from the second register can be transferred to the first register. With this system, image data can be corrected with a simple circuit structure.
In the image display apparatus described above, the second register can be a shift register, and correction data can be read by direct sequential shifting one bit at a time. This eliminates the need for data bus line branching to transfer correction data, and it also eliminates the need for an address bus to select buffer memory.
The image display apparatus of the present invention can use LEDs as the light emitting devices. In this image display apparatus, LED display peripheral circuit structure can be simplified and the display apparatus can made compact.
Finally, the image display apparatus of the present invention can display images by dividing the entire image into parts. Since the image display apparatus of the present invention can simplify peripheral circuit structure, it is suitable for use in image data units which display part of an entire image, for example, it is suitable for LED units used in large-scale LED displays.